The invention relates to a rotary electric machine, particularly a motor vehicle alternator, of the type comprising a front bearing and a rear bearing on which stator windings are fixed and in which a rotor shaft is mounted so that it can rotate, a rectifier arrangement comprising a number of positive diodes supported by a heat dissipater in the overall form of a support plate and a number of negative diodes supported by a support element in the form of a plate, these plates being axially juxtaposed and fixed to the rear bearing, and a device affording cooling by circulating an axial stream of a cooling fluid, such as air, through axial openings in said plates, at least some openings in the plate supporting the positive diodes being provided with cooling ribs. Advantageously, the plate supporting the negative diodes forms part of the rear bearing.
An electric machine of this type is described in document DE-A-19705228. The openings which are made in the plate supporting the positive diodes comprise five openings of significant angular aperture two of which have a trapezoidal overall shape. These trapezoidal openings are each surrounded by a rib projecting axially from the plate.
This cooling device with axial openings admittedly affords more effective cooling than cooling devices without axial openings, but is still not satisfactory.
The same is true of the cooling device described in document U.S. Pat. No. 5,646,838.
In that document, the plate supporting the positive diodes comprises a great many ribs which have the shape of fins extending practically radially across the plate; an opening for the passage of cooling air being provided between each pair of adjacent fins. The fins extend from the inner edge of the support plate and some distance from the outer periphery of the plate and from the positive diodes; the plate being thicker in the region of the fins.
The object of the invention is to improve the cooling of a rotary machine of the abovementioned type.
To achieve this objective, the machine of the invention is characterized in that first fins extend practically as far as the outer periphery of the plate supporting the positive diodes so that the plate is cooled across its entire radial stretch.
According to another feature of the invention, at least two positive diodes are arranged near the outer periphery of the plate supporting the positive diodes and second fins extend as far as said diodes and close to them. By virtue of this arrangement, the openings can be formed radially under the diodes and the thickness of the plate can be increased at the diodes to allow better cooling of these diodes. Furthermore, the second fins participate in the cooling.
According to yet another feature of the invention, the openings in the plate supporting the positive diodes constitute, with the fins which delimit them, channels for the accelerated flow of cooling air.
Advantageously, at least a first fin is near a positive diode in order to cool the latter even better still.
Advantageously, the rotary electric machine comprises a cover part which, in the region of the fins of the plate supporting the positive diodes, has radial openings corresponding to those of the plate supporting the positive diodes.
These openings are delimited by strips of material or narrow radial ribs. The thickness of these ribs is dependent on the thickness of the fins, the ribs being arranged under the fins. This yields communication between the openings of cover and those of the plate supporting the positive diodes.
The openings of the cover have a greater radial span than those of the plate supporting the positive diodes.
Advantageously, the openings in the cover are split into two by a strip of material or coaxial, that is to say circumferential, ribs. A first part of the openings in the cover faces the passage openings in the plate supporting the positive diodes, the second part of the openings being located at the outer periphery of the cover.